1. Field of the Invention
The present invention relates to a magnetoresistive head for use in a magnetic recording device such as a magnetic disk drive and a magnetic tape drive.
2. Description of the Related Art
In association with a reduction in size and an increase in recording density of a magnetic disk drive in recent years, the flying height of a head slider has become smaller and it has been desired to realize contact recording/reproduction such that the head slider flies a very small height above a recording medium or comes into contact with the recording medium. Further, a conventional magnetic induction head has a disadvantage such that its reproduction output decreases with a decrease in peripheral speed of a magnetic disk as the recording medium (relative speed between the head and the medium) caused by a reduction in diameter of the magnetic disk. To cope with this disadvantage, there has recently extensively been developed a magnetoresistive head (MR head) whose reproduction output does not depend on the peripheral speed and capable of obtaining a large output even at a low peripheral speed. Such a magnetoresistive head is now a dominating magnetic head. Further, a magnetic head utilizing a giant magnetoresistive (GMR) effect is also commercially available at present.
With higher-density recording in a magnetic disk drive, a recording area of one bit decreases and a magnetic field generated from the medium accordingly becomes smaller. The recording density of a magnetic disk drive currently on the market is about 10 Gbit/in2, and it is rising at an annual rate of about 200%. It is therefore desired to develop a magnetoresistive sensor and a magnetoresistive head which can support a minute magnetic field range and can sense a change in small external magnetic field.
At present, a spin valve magnetoresistive sensor utilizing a spin valve GMR effect is widely used in a magnetic head. In such a magnetoresistive sensor having a spin valve structure, a magnetization direction in a free ferromagnetic layer (free layer) is changed by a signal magnetic field from a recording medium, so that a relative angle of this magnetization direction to a magnetization direction in a pinned ferromagnetic layer (pinned layer) is changed, causing a change in resistance of the magnetoresistive sensor.
In the case of using this magnetoresistive sensor in a magnetic head, the magnetization direction in the pinned layer is fixed to a direction along the height of a magnetoresistive element, and the magnetization direction in the free layer in the condition where no external magnetic field is applied is generally designed to a direction along the width of the magnetoresistive element, the direction which is perpendicular to the pinned layer.
Accordingly, the resistance of the magnetoresistive sensor can be linearly increased or decreased according to whether the direction of the signal magnetic field from the magnetic recording medium is parallel or antiparallel to the magnetization direction of the pinned layer. Such a linear resistance change facilitates signal processing in the magnetic disk drive.
In the conventional magnetoresistive sensor, a sense current is passed in a direction parallel to the film surface of the magnetoresistive element to read a resistance change according to an external magnetic field. In such a case of a CIP (Current In the Plane) structure that a current is passed in a direction parallel to the GMR film surface, the output from the sensor decreases with a decrease in sense region defined by a pair of electrode terminals. Further, in the spin valve magnetoresistive sensor having the CIP structure, insulating films are required between the GMR film and an upper magnetic shield and between the GMR film and a lower magnetic shield.
That is, the distance between the upper and lower magnetic shields is equal to the sum of the thickness of the GMR film and a value twice the thickness of each insulating film. At present, the thickness of the insulating film is about 20 nm at the minimum. Accordingly, the distance between the upper and lower magnetic shields becomes equal to the sum of the thickness of the GMR film and about 40 nm.
However, with this distance, it is difficult to support a reduction in length of a recording bit on the recording medium, and the current CIP spin valve magnetoresistive sensor cannot meet the requirement that the distance between the magnetic shields is to be reduced to 40 nm or less. In these circumstances, it is considered that a magnetic head having a CIP structure utilizing a spin valve GMR effect can support a recording density of 20 to 40 Gbit/in2 at the maximum. Even by applying specular scattering as a latest technique, the maximum recording density is considered to be 60 Gbit/in2.
As mentioned above, the increase in recording density of a magnetic disk drive is rapid, and it is expected that a recording density of 80 Gbit/in2 will be desired by 2002. When the recording density becomes 80 Gbit/in2 or higher, it is very difficult to support such a high recording density even by using a CIP spin valve GMR magnetic head to which the latest specular scattering is applied, from the viewpoints of output and the distance between the magnetic shields. As a post spin valve GMR intended to cope with the above problem, there have been proposed a tunnel MR (TMR) and a GMR having a CPP (Current Perpendicular to the Plane) structure such that a current is passed in a direction perpendicular to the GMR film surface.
The TMR has a structure that a thin insulating layer is sandwiched between two ferromagnetic layers. The amount of a tunnel current passing across the insulating layer is changed according to the magnetization directions in the two ferromagnetic layers. The TMR shows a very large resistance change and has a good sensitivity, so that it is expected as a promising post spin valve GMR. On the other hand, in the case of the GMR having the CPP structure, the output increases with a decrease in sectional area of a portion of the GMR film where a sense current is passed. This feature of the CPP structure is a large advantage over the CIP structure.
The TMR is also considered to be a kind of CPP structure, because a current is passed across the insulating layer from one of the ferromagnetic layers to the other ferromagnetic layer. Therefore, the TMR also has the above advantage. For the purpose of higher sensitivity in the GMR having the CPP structure, it has been proposed to make the sizes of two electrode terminals sandwiching the GMR film smaller than the size of the GMR film (Japanese Patent Laid-open No. 10-55512).
In a manufacturing method for the magnetoresistive head described in the above publication, one of the two electrode terminals is first formed, the GMR film is next formed, and the other electrode terminal is next formed. However, in fabricating a microstructural GMR element at present, it is very difficult to make the sizes of the two electrode terminals smaller than the size of the GMR film and to suppress misalignment by adopting the above conventional manufacturing method.
In a conventional MR head manufacturing method (the term of MR in this specification including GMR), an MR head is manufactured by a contact hole process or a lift-off process. In the contact hole process, an MR film is formed into a desired shape, and a magnetic domain control film and an insulating film are next laminated. Thereafter, a contact hole is formed to electrically connect an upper electrode terminal and the MR film. In the lift-off process, a photoresist for patterning an MR film is left, and a magnetic domain control film and an insulating film are laminated. Thereafter, the photoresist is removed to thereby form a contact hole for electrically connecting an upper electrode terminal and the MR film.
The MR film at present has a width of about 0.1 xcexcm. On the other hand, the photolithography technique at present has an error of about 0.06 xcexcm. Accordingly, as the MR film becomes more microscopic, alignment of the MR film and the contact hole becomes difficult in the conventional contact hole process. On the other hand, the lift-off process also has a problem of defective contact or the like because a part of the photoresist remains after lift-off.
It is therefore an object of the present invention to provide a magnetoresistive head which can obtain a high reproduction output signal.
It is another object of the present invention to provide a magnetoresistive head manufacturing method which can manufacture such a magnetoresistive head easily at a high yield.
In accordance with an aspect of the present invention, there is provided a magnetoresistive head comprising a first magnetic shield; a first electrode terminal provided on said first magnetic shield, said first electrode terminal having a first width; a magnetoresistive film provided on said first electrode terminal, said magnetoresistive film having a second width less than or equal to said first width; a second electrode terminal provided on said magnetoresistive film, said second electrode terminal having a third width less than or equal to said second width; and a second magnetic shield provided on said second electrode terminal.
In accordance with another aspect of the present invention, there is provided a magnetoresistive head comprising a first magnetic shield; a first electrode terminal provided on said first magnetic shield, said first electrode terminal having a first height; a magnetoresistive film provided on said first electrode terminal, said magnetoresistive film having a second height less than or equal to said first height; a second electrode terminal provided on said magnetoresistive film, said second electrode terminal having a third height less than or equal to said second height; and a second magnetic shield provided on said second electrode terminal.
Preferably, a pair of magnetic domain control films are provided on the opposite sides of the magnetoresistive film, and the first magnetic shield is provided on a substrate. More preferably, the magnetoresistive head further comprises a plug electrode for connecting the second electrode terminal and the second magnetic shield, and a plug side wall protective insulating film for covering a side wall of the plug electrode.
In accordance with a further aspect of the present invention, there is provided a magnetoresistive head comprising a first electrode terminal serving also as a first magnetic shield, said first electrode terminal having a first width; a magnetoresistive film provided on said first electrode terminal, said magnetoresistive film having a second width less than or equal to said first width; a second electrode terminal provided on said magnetoresistive film, said second electrode terminal having a third width less than or equal to said second width; and a second magnetic shield provided on said second electrode terminal.
In accordance with a still further aspect of the present invention, there is provided a magnetoresistive head comprising a first electrode terminal serving also as a first magnetic shield, said first electrode terminal having a first height; a magnetoresistive film provided on said first electrode terminal, said magnetoresistive film having a second height less than or equal to said first height; a second electrode terminal provided on said magnetoresistive film, said second electrode terminal having a third height less than or equal to said second height; and a second magnetic shield provided on said second electrode terminal.
In accordance with a still further aspect of the present invention, there is provided a manufacturing method for a magnetoresistive head, comprising the steps of forming a first magnetic shield; forming a first electrode terminal on said first magnetic shield; forming a magnetoresistive film on said first electrode terminal; forming a first film for forming a second electrode terminal on said magnetoresistive film; forming a second film for forming a plug electrode on said first film; applying a photoresist to said second film; patterning said photoresist to a desired shape; etching said second film by using said patterned photoresist as a mask to form said plug electrode having a desired shape; removing said patterned photoresist and next depositing a first insulating film on said first film so as to cover said plug electrode; etching back said first insulating film by isotropic etching to form a first plug side wall protective insulating film for covering said plug electrode; etching said first film by ion milling by using said first plug side wall protective insulating film as a mask to form said second electrode terminal having a desired shape; depositing a second insulating film on said magnetoresistive film so as to cover said first plug side wall protective insulating film; etching back said second insulating film by isotropic etching to form a second plug side wall protective insulating film for covering said first plug side wall protective insulating film; and etching said magnetoresistive film into a desired shape by using said second plug side wall protective insulating film as a mask.
Preferably, the manufacturing method for the magnetoresistive head further comprises the steps of depositing a magnetic domain control film on said first electrode terminal so as to cover said second plug side wall protective insulating film after said step of etching said magnetoresistive film; etching back said magnetic domain control film by ion milling to obtain a desired shape and thickness; depositing an interlayer insulating film on said first electrode terminal and said magnetic domain control film; planarizing said interlayer insulating film; forming a through hole for said first electrode terminal in said interlayer insulating film; and forming a second magnetic shield on said interlayer insulating film so that said second electrode terminal is connected through said plug electrode to said second magnetic shield, and said first electrode terminal is connected directly to said second magnetic shield in said through hole. Thus, the second electrode terminal is connected through the plug electrode to the second magnetic shield, and the first electrode terminal is connected directly to the second magnetic shield in the through hole.
In the magnetoresistive head of the present invention, the height or width of the first electrode terminal can be made larger than the height or width of the magnetoresistive film. Accordingly, there is almost no need for alignment of the first electrode terminal and the second electrode terminal and for alignment of the first electrode terminal and the magnetoresistive film, thereby facilitating the fabrication of the magnetoresistive head.
Although the height or width of the first electrode terminal is set larger than the height or width of the magnetoresistive film, there is no effect on reproduction characteristics. Further, in the case that the height or width of the first electrode terminal is equal to the height or width of the magnetoresistive film, the first electrode terminal and the magnetoresistive film can be formed simultaneously, thereby facilitating the fabrication of the magnetoresistive head. In the case that the height or width of the second electrode terminal is less than the height or width of the magnetoresistive film, the sectional area of a portion of the magnetoresistive film where a sense current flows can be reduced, thereby obtaining a high reproduction output in view of the characteristics of a CPP structure.
In the case that the height or width of the second electrode terminal is equal to the height or width of the magnetoresistive film, the second electrode terminal and the magnetoresistive film can be formed simultaneously, thereby facilitating the fabrication of the magnetoresistive head. Further, in the case that the height or width of the second electrode terminal is less than the height or width of the magnetoresistive film, self-alignment can be effected by a process technique such as photoresist shrinkage, so that alignment of the second electrode terminal and the magnetoresistive film is not required, thereby facilitating the fabrication of the magnetoresistive head.
In the structure that the height or width of only the second electrode terminal is less than the height or width of the magnetoresistive film according to the present invention as compared with the conventional structure disclosed in Japanese Patent Laid-open No. 10-55512 that both the first and second electrode terminals are smaller in size than the magnetoresistive film, higher current concentration occurs to thereby obtain a similar or higher reproduction output.
Accordingly, also in forming a microstructural magnetoresistive element supporting a high recording density, alignment of the two electrode terminals sandwiching the magnetoresistive film is not required, thereby facilitating the fabrication of the magnetoresistive element. Further, the magnetoresistive element can be manufactured at a high yield, and a high reproduction output signal with no Barkhausen noise can be obtained.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.